Hereafter, a wireless transmit/receive unit (WTRU) includes but is not limited to a user equipment (UE), mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, a base station includes but is not limited to a Node-B, site controller, access point or any other type of interfacing device in a wireless environment.
The 3GPP has lately initiated the Long Term Evolution (LTE) program to bring new technology, new network architecture and configuration and new applications and services to the wireless cellular network in order to provide improved spectral efficiency, reduced latency, faster user experiences and richer applications and services at less cost.
With the advances of both wireless technology and internet technology, the integration of these two technologies and applications are the focus of the telecom industry. Given that the Internet Multimedia System (IMS) has already been specified, designed and implemented, tighter integration of the IMS into the current 3GPP and the future LTE takes on even greater importance. It is foreseeable that in the LTE network, WTRUs will be equipped with the IMS software and hardware and need to be a part of the system normal operation, including system initiation and registration.
It has been proposed for the LTE project that to reduce end-user latency, user and control plane separation in the Radio Access Network (RAN) should be implemented to optimize routing of user-plane and control-plane data. Similar concepts are applicable to Evolved High Speed Packet Access (HSPA) systems.
In current wireless telecommunication systems, when a WTRU switches on from the power-off state and gets camped with a cell, the WTRU will register itself to the network to obtain the subscribed services. This step is usually referred to as the ATTACH procedure, where the WTRU gets authenticated by the network and the network is updated as to where the WTRU is located. Subsequently, the WTRU is able to invoke outgoing calls and receive incoming calls via paging. Recently, this ATTACH procedure is even able to obtain an IP address for the mobile device, whereby direct dialog with another internet device is made possible by the extended ATTACH procedure.
However, this extended ATTACH procedure has not provided help for the prevailing IMS service, For any IMS enabled mobile device, additional steps/procedures beyond the ATTACH procedure are still required to make the mobile device IMS serviceable. As will be set forth below in the description of FIG. 1A, there is no provision for SIP Registration, which has to be performed after, and independently of, the extended ATTACH procedure, thereby preventing immediate use of the IMS service by the WTRU.
Without the SIP registration, the mobile device is further unable to receive incoming IMS (VoIP) calls and cannot set up any outgoing calls until the SIP Registration and IMS authentication is successfully completed.
Currently there is no specified approach for performing SIP Registration in synchronism with the completion of the ATTACH procedure, the result being that SIP Registration and subsequent IMS authentication are neither immediately nor automatically performed after the ATTACH procedure.
The inability to make IMS service available upon power up is due to the separation of the WTRU ATTACH procedure, shown in FIG. 1A, from the WTRU IMS SIP Registration, shown in FIG. 1B. On the user equipment side, the IMS SIP Registration is not part of the initial ATTACH procedure to attach the WTRU to the network. Also, the SIP Registration, as per the current WTRU ATTACH procedure, must await completion of the ATTACH procedure. In addition, the SIP Registration is not specified to immediately follow completion of the ATTACH procedure.
Considering all of the above, the IMS service cannot be used immediately after the WTRU powers up and users may have longer waiting times before the IMS service is ready for use. The separation of the SIP Registration and the ATTACH procedure also increases the number of signaling messages traveling between the WTRU and the E-Core, adding unnecessary network traffic load, both over the air and on landlines.